World

Northern Great Barrier Reef in midst of worst bleaching event on record

Australian scientists have confirmed what they have feared for months as a global coral bleaching event hit one ecological treasure after another, from Hawaii to Indonesia.

In a press release on March 29, the Australian Coral Bleaching Task Force announced that the northern portions of the Great Barrier Reef are in the throes of the most intense coral bleaching event on record there.

These parts of the reef contain some of the most pristine sections of the World Heritage site and are a major tourism draw for Australia.

Coral bleaching of the Great Barrier Reef viewed from the air.

Image: Coral bleaching task force

The Task Force, comprised of 10 Australian research institutions, made its determination after completing aerial surveys of more than 500 coral reefs from Cairns north to Papua New Guinea.

“This has been the saddest research trip of my life,” says Prof. Terry Hughes, convener of the National Coral Bleaching Taskforce, said in a press release.

“Almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef," Hughes said.

"We flew for 4,000 kilometers in the most pristine parts of the Great Barrier Reef, and saw only four reefs that had no bleaching. The severity is much greater than in earlier bleaching events in 2002 or 1998.”

Observations from ocean-going vessels and research stations confirmed the findings made from the air, which is that the majority of reefs north of Cairns are undergoing bleaching, including all species of corals.

“Even more concerning, we haven’t yet found the southern limit of the bleaching,” Hughes said.

Trend in global ocean heat content anomalies since 1950.

Image: noaa

All but four of the reefs surveyed were undergoing severe bleaching, which is an extraordinarily high number, said Mark Eakin, the coordinator of Coral Reef Watch for the National Oceanic and Atmospheric Administration (NOAA) in Maryland.

“It’s a little surprising," Eakin told Mashable in an interview, regarding the severity of the bleaching throughout the northern Great Barrier Reef. "What they’re seeing is really severe,” he said.

The ongoing global bleaching event is the longest-lasting one ever observed, and only the third ever seen. It has occurred during the warmest year on record, which occurred in 2015, and the two most unusually mild months on Earth, which took place in January and February, respectively.

“This has been the saddest research trip of my life”

It is due to record warm ocean temperatures around the world, partly driven by a strong El Niño event in the tropical Pacific Ocean.

However, human-caused global warming is also boosting ocean temperatures and making ocean waters more acidic, causing challenges for coral reefs.

According to Eakin, the ongoing event may last into 2017, as projections show that coral bleaching will soon spread into the Indian Ocean and then reach the Caribbean this summer.

“We’ll be conducting further aerial surveys this week in the central Great Barrier Reef to identify where it stops," Hughes said.

Southern parts of the reef are thought to have escaped bleaching for now, at least, due to cloudy weather that kept water temperatures down.

Bleached coral in the Great Barrier Reef.

Image: coral reef task force

Coral bleaching occurs when unusual environmental conditions, such as heightened ocean temperatures, cause corals to expel tiny photosynthetic algae, called zooxanthellae. It is these algae that give corals their vibrant colors and allow them to play host to such a diverse array of marine life.

The loss of these algae causes the corals to turn white, and bleach. Bleached corals can recover if the water temperature drops and zooxanthellae are able to recolonize them over a period of time. However, if temperatures remain elevated or algae otherwise fails to return, the coral may die.

“We could see extensive bleaching even among the most robust ‘massive’ corals,” says James Kerry, Project Manager of the National Coral Bleaching Taskforce, who also participated in the aerial surveys. “The fact that these hardy species have also turned white shows just how severe summer conditions have become on the northern GBR.

“Residents we spoke to in Cape York were shocked by what they are seeing, telling us that they had never experienced anything like this before.”

Scientists have already reported up to 50% mortality of bleached corals, but the permanence of the damage from this event is not yet clear, since the bleaching event will continue for the next several months, according to the Task Force as well as Eakin, who helps produce bleaching forecasts around the world.

According to Eakin, coral bleaching is ongoing throughout much of the southern hemisphere right now, including around Indonesia, near Reunion Island off the coast of Africa, throughout the reefs off the coast of New Caledonia, along with the island nation of Kiribati.

Bleached coral in Hawaii in late 2014.

Image: XL Catlin Seaview survey

In Lizard Island, Australia, to the northeast of Cairns, officials are estimating that 50% of the reefs have been killed due to prolonged and intense bleaching. “That is going to have a major impact ecologically, much more than just bleaching alone,” Eakin said.

Around Christmas Island, which is about 490 kilometers, or 300 miles, south of Jakarta, Indonesia, coral bleaching has been ongoing since June of 2015, Eakin said.

“This is a really wide and encompassing event,” he said, that is likely to get worse before it gets better.

The reason is that weather patterns connected to El Niño, as well as independent patterns, are now coming into play in areas not yet touched by the bleaching event, including the Maldives.

“These effects put into place are going to be lasting for several more months,” Eakin said.

Coral bleaching outlook from April through July 2016.

Image: NOAA Coral reef watch

In Hawaii, coral bleaching is finally subsiding, but the damage may be long-lasting, Eakin said, with some 500-year-old reefs seeing 95% mortality.

“It’s gonna be a long-term impact on those reefs,” he said.

So far, this coral bleaching event is about on par with past ones in terms of global severity, Eakin said, but the longevity of this one stands out.

"Past global bleaching events transpired over course of a year. This event has been going on since June of 2014, and we’ve never seen anything like that before," adding: “We’re nowhere close to being finished with this event.”

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